It is required for an electric device to protect the device from water, i.e., high water-resistant reliability is required for the electric device. To protect the device, hot melt resin is coated on an outer surface of the device as an object to be protected from water. This structure is defined as a hot melt water-resistant structure. For example, JP-A-2002-184513 discloses this structure. Specifically, hot melt adhesive is applied to an inner wall of a heat-shrinkable tube, and a connection portion of a cable is covered with the heat-shrinkable tube. FIG. 16 shows a conventional hot melt water-resistant structure composed of a casing 100 for accommodating an electric device, a wiring member 200 and a resin cover 300 for covering the casing 100. The wiring member 200 has a film shape, and protrudes from the casing 100. The resin cover 300 is made of hot melt resin, and covers the whole outer surface of the casing 100 as an object to be protected from water.
However, when an electric device has a casing for accommodating a large-scale printed circuit board, the area of the whole outer surface of the casing as an object to be covered by hot melt resin becomes large. Accordingly, the amount of hot melt resin increases although the unit price of the hot melt resin is high. Thus, the manufacturing cost of the device becomes large. Further, heat generated in the printed circuit board increases, so that performance of an electric circuit on the board may be reduced.
Thus, it is required for the hot melt water-resistant structure to reduce its manufacturing cost and to improve water-resistant reliability.